The following correction was printed in the Observer's For the record column, Sunday 12 July 2009

In the article below, we misquoted Rudyard Kipling's poem "The Young British Soldier". "When you're left wounded on Afghanistan's plains" should have been "When you're wounded and left on Afghanistan's plains" and the correct "An' go to your Gawd like a soldier" was changed to "And go to your Gawd ..."

When you're left wounded on Afghanistan's plains And the women come out to cut up what remains Jest roll to your rifle and blow out your brainsAnd go to your Gawd like a soldier

There's no heroism to be found in "The Young British Soldier", Kipling's poem written after the Afghan war of the 1880s: simply acknowledgement of the country's mythic savagery and resilience, which must prompt us to ask again if the sacrifices being made by British infantry in Helmand, most recently by Lieutenant Colonel Rupert Thorneloe and Trooper Joshua Hammond, have any more lasting purpose than the conflicts of Empire?

Other questions follow. Will the American surge of 10,000 troops master the province we have struggled to subdue? Is there an overall workable strategy in place? And can we afford the cost of the war and the lives lost?

No flicker of doubt seems to exist in the soldiers' minds: a few days before he was blown up with Hammond and six other men, the much admired Thorneloe gave an interview in which he didn't question the mission. Nor did he complain about his men's equipment, though if the British had had the helicopters the Americans have brought with them, he might not have been travelling in the much criticised Viking armoured vehicle.

The politicians seem equally certain. Last year David Miliband said: "Sixty or seventy years ago the armed forces defended Britain on the white cliffs of Dover. Now to defend Britain we have got to be in the toughest areas of the world ... So the purpose of the mission is absolutely clear. It is to make a sure that Afghanistan does not become a safe haven for people who want to plot against the UK."

Is it really as straightforward as that? Ten days ago in a public interview with Graydon Carter, the editor of Vanity Fair, in New York, Tony Blair recalled the speech he made in Chicago a decade earlier, when he outlined his ideas on liberal interventionism - "the right to intervene for humanitarian purposes ... and to remove a regime that was brutalising its people". How much is liberal interventionism still riding in the sidecar of this mission? A lot has been said about the cruelty of the Taliban, the children attending schools for the first time and the building of a civil society with elections due in August. Is this simply about "winning hearts and minds", or do the residues of Blair's Chicago doctrine still lurk?

This is a good moment to recall the theory of Gilles Dorronsoro of the Carnegie Endowment for International Peace, who wrote in January: "The mere presence of foreign soldiers fighting a war in Afghanistan is probably the single most important factor in the resurgence of the Taliban." That same point was hinted at by a British commander quoted in Patrick Bishop's book, Ground Truth. Brigadier Mark Carleton-Smith, who led 16 Air Assault to Helmand, made an odd aside in a report back to London before the real trouble began: "There is not to my mind an insurgency in Helmand. But we can create one if we want to."

The idea that we might be creating a war by stimulating resistance is haunting, especially when you learn from The Power of Numbers, to be published by Policy Exchange this week, that the average age in Afghanistan is 16. Compare that to the average age of Americans (35) and Europeans (38) and you see the enormous advantage the Taliban have in a country that is full of young men and where life is cheap. We are apt to forget the society we seek to influence and the lives affected in the process.

The British toll has reached 171, with many more wounded and maimed. We have a constant responsibility to review our presence in Afghanistan even though most policymakers continue to believe that containment of the Taliban and al-Qaida several thousand miles away is an acute issue of national defence. But we can't do that if there is no clear strategy, and resources are diminishing.

"We are wasting precious lives," says Paddy Ashdown, who until January was to be the UN's plenipotentiary in Afghanistan, "because our politicians will not get their act together. Unless there is a single strategy operating to a single set of priorities, speaking with a single voice, we are not going to win this battle."

The fear is that we have drifted from a policy of extending control and consolidation - "take, hold and build" - to a point where we can only hope to contain, with all the senseless loss that entails.

It all comes down to resources, which are threatened as never before, because of the collapse of public finances. "The armed forces we had," a recently retired general told me, "were designed to do one medium-scale enduring operation. So the big strategic mistake was when we committed ourselves to Afghanistan when we were already committed to Iraq. Inevitably we were not going to have the resources to do either properly. "

This is where the military feel the punishing impact of Blair's liberal interventionism, what the general describes as a "fantastic amount of wishful thinking" when it came to matching aspiration with resources. "The military is like a business. We were quite well capitalised but now we need to rebuild the business. We are losing trained and experienced people because individually they have decided that they've had enough and don't want to do it [Afghanistan] again."

Rebuilding seems unlikely, given the government's prioritisation - and indeed the opposition's - of frontline services over the real frontline in Afghanistan. In a review for the Royal United Services Institute last week, Malcolm Chalmers says the best estimate is that the Ministry of Defence will make a real-terms cut over the next six years of 10%-15%. But if the economy fails to recover, even taxes may not prevent deeper cuts. That would bring our military to the level of that of Belgium or Holland, according to the general. Fighting a war in Afghanistan would be almost out of the question.

"Why is it that other countries are able to give their armed forces what they need," asked Liam Fox, the shadow defence secretary, after Thorneloe's death, "when they need it and where they need it, but under the current government we are unable to do the same?"

He knows the answer: the money has gone elsewhere - an 85% increase in spending on health over the past decade, 63% on education and 50% on public security and order. And he knows that his party can do little to alter circumstances where spending on public order and safety has risen to nearly equal the defence budget.

What is disturbing, and why Ashdown says that a defence review is a day one item on the next prime minister's desk, is the possibility of an overspend of about 27% of the entire annual defence budget. Meanwhile, the general observes: "The world is becoming increasingly unstable and dangerous. To put your finances in such a state that you cannot afford to defend the country properly seems to be very irresponsible."

I cannot help thinking that a lot of that responsibility lies with the man I watched in New York explaining his mission to intervene. We must wonder to what extent intervention, for whatever reason, is the cause of rather than the solution to the old problem of Afghanistan.